Heterotrimetallic Carbon Dioxide Copolymerization and Switchable Catalysts: Sodium is the Key to High Activity and Unusual Selectivity.

A challenge in polymer synthesis using CO is to precisely control CO placement in the backbone and chain end groups. Here, a new catalyst class delivers unusual selectivity and is self-switched between different polymerization cycles to construct specific sequences and desirable chain-end chemistries. The best catalyst is a trinuclear dizinc(II)sodium(I) complex and it functions without additives or co-catalysts. It shows excellent rates across different ring-opening (co)polymerization catalytic cycles and allows precise control of CO incorporation within polyesters and polyethers, thereby allowing access to new polymer chemistries without requiring esoteric monomers, multi-reactor processes or complex post-polymerization procedures. The structures, kinetics and mechanisms of the catalysts are investigated, providing evidence for intermediate speciation and uncovering the factors governing structure and composition and thereby guiding future catalyst design.